Two forms of parathyroid hormone‐like adenylate cyclase‐stimulating protein derived from tumors associated with humoral hypercalcemia of malignancy

Tumors associated with humoral hypercalcemia of malignancy (HHM) contain parathyroid hormone‐like adenylate cyclase‐stimulating proteins (hACSPs). We previously purified a 17,000 MW hACSP from an HHM‐associated breast carcinoma. This report describes the characterization of hACSPs from three additional HHM‐associated tumors: two typical HHM‐associated tumors (squamous carcinomas) and a third unusual tumor type (pheochromocytoma). Each tumor was extracted in acid‐urea/ethanol‐sodium chloride, and adenylate cyclase‐stimulating activity (ACSA) was examined following reverse‐phase and size‐exclusion HPLC and isoelectric focusing. Each tumor contained a high molecular weight form of ACSA which co‐eluted with the 17,000 molecular weight breast carcinoma hACSP in each of the three separation procedures. Each also contained a lower molecular weight form(s) of ACSA (6,000–9,000 molecular weight). Both forms were inhibited by Nle^8,18Tyr³⁴bPTH(3–34) amide. The high molecular weight form was not changed to the lower molecular weight form by a reducing agent. Some HHM‐associated tumors contain two forms of hACSP, one with a molecular weight of 17,000 and another with a molecular weight of 6,000–9,000, which appears to be an amino‐terminal cleavage product of the larger protein.